This invention relates to a novel underwater blasing method for removing safely and economically underwater obstacles on the beds of lakes and seas by blasting with a fluid explosive.
In recent years, sea development and bridge construction have greatly increased. These proejcts necessitate effective removal by blasting of obstacles lying on the bottom of the sea or lake. In the past, use has been made of the so-called "boring and blasting method" wherein blasting holes are drilled in the obstacle to be removed and a plastic or solid explosive loaded in the holes for blasting away the obstacle. However, this method has not been satisfactory from the standpoint of safety and economy.
For example, in the underwater blasting method generally followed in the prior art, a solid or plastic explosive such as dynamite or the like has ordinarily been employed. Because these explosives are difficult to load tightly into blasting holes, it is necessary to drill many blasting holes in those underwater blasting operations where a large amount of an explosive is required. Consequently, many days and considerable expense were required for the hole drilling.
The operations involved in loading a solid or plastic explosive charge in blasting holes and then detonating the charge can be done comparatively safely on dry land by loading the bulk of the explosive charge in each hole, then loading the so-called "parent explosive cartridge" having at one terminal end a detonator, and finally firing the detonator. In contrast, such work is difficult to perform underwater and a very dangerous method has been adopted wherein the entire explosive charge including the detonating device is then loaded into blasting holes by lowering it down through the water.
Furthermore, in previous underwater blasting methods employing a solid or plastic explosive, there was a very dangerous and difficult problem on disposing of residual explosive after a misfire.
In practicing underwater blasting, the use of a fluid explosive is considered more advantageous than a solid or plastic explosive in respect to loading the explosive in blasting holes and in the dispositon of any misfired residual explosive. However, an underwater blasting method using a fluid explosive has not yet been developed. In addition, only an extremely small number of fluid explosives proposed hitherto are practically applicable. As seen in the case of nitroglycerin, some fluid explosives are chemically unstable and tend to be too sensitive to shocks and friction. Thus, many of the liquid exlosives are dangerous to manufacture and handle.
One highly practical known slurry explosive is a super-saturated aqeuous solution of ammonium nitrate incorporated with trinitrotoluene or powdery aluminum. However, this slurry explosive has the drawbacks that the solubility of ammonium nitrate in water is not high and its solubility is greatly affected by the temperature so that the ammonium nitrate can crystallize out and greatly change the explosive properties when the temperature falls during storage.